This disclosure relates generally to precharging when starting an electric vehicle. More particularly, this disclosure relates to varying a precharge time under some conditions, such as by increasing a time spent precharging.
Example electric vehicles include hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), and mild hybrid vehicles (mHEVs). Generally, hybrid vehicles differ from conventional vehicles because hybrid vehicles are selectively driven using a battery-powered electric machine. Conventional vehicles, by contrast, rely exclusively on an internal combustion engine to drive the vehicle.
An electrical power source, such as a battery, can be used to power a powertrain of an electric vehicle. Power from the battery is transferred to the electric machine. When the electric vehicle is off, the battery is disconnected from the rest of powertrain via contactors, for example. At start-up, the battery is reconnected to the portions of the powertrain.
The powertrain of an electric vehicle has significant capacitance. The capacitance has a very low resistance and can cause a large amount of in-rush current when the battery is reconnected and the capacitance charges. High in-rush current can damage components. Thus, many powertrains incorporate a precharge circuit to limit the in-rush current during the initial phase of start-up. The precharge circuit may incorporate a precharge contactor and resistor. The precharge circuit limits in-rush current by routing current through the precharge resistor.
As the capacitance is charged, the current decreases to a point where a main contactor, without the large resistance, can be connected. Prior art vehicles measure voltage to determine when to disconnect the precharge contactor.